**1. Introduction**

Part one of this series showed that process engineering characterisation is essential for understanding and optimising bioreactors and bioprocesses for the biopharmaceutical industry. Process engineering characterisation usually includes determining the specific power input *P=V*, hydrodynamic stress *τ*, mixing time Θ*m*, volumetric oxygen mass transfer coefficient *k*L*a* and, if applicable, the *N*S1 criterion. Determining these parameters by computational fluid dynamics (CFD) and the experimental investigation of the parameters, which serves as validation, were both described in part one. Furthermore, the literature review of 50 publications showed that Ansys Fluent and OpenFOAM are among the most widely used software solutions for CFD applications in biotechnology. Using selected, practice-relevant examples from the authors' research, the second part of the series now demonstrates how process engineering characterisation can be carried out using CFD and then be validated with experimental investigations. The two most frequently used software solutions were selected for the investigations. In Section 2, the specific power input is determined for two stirred reactors with different working volumes and stirrer configurations. This was then validated experimentally by measuring the electric current and the torque, which were then used to determine the specific power input. The determination of the *k*L*a* value by coupling population balance modelling and CFD is also presented for a stirred bioreactor and compared with the gassing-out method. In Section 3, the Flexsafe RM 2 L basic single-use bioreactor bag from Sartorius AG is used to demonstrate how the specific power input and the hydrodynamic stress in a wave-mixed bioreactor system can be determined. Particle image velocimetry (PIV) was used for validation. In Section 4, the influence of the contact angle, which is material-dependent, on the specific power input in shake flasks is investigated. For this example, the sickle height was used for validation purposes and compared with experiments and semiempirical formulas.
